GROUP SIZE: Small or Individual
TIME: 2-45 minute periods
TYPE OF ACTIVITY: Student Investigation
TEACHING STRATEGY: Guided Discovery Expository
CONCEPTS: Tropism Artificial Gravity Stimulus/Response
SKILLS: Experimentation Collecting and Interpreting Data
Objectives: To show tropism in plants and to show the effect of artificial gravity on the growth of plants.
- (Activity 1) Lima bean seedlings; three test tubes; test tube clamps and ring stand; water; stoppers with hole.
- (Activity 2) Several kinds of seeds – lima beans, corn, radish, etc.; glass jars; paper toweling.
- (Activity 3) Phonograph turntable; several soil-less containers with plants (You may use the same setup as in Activity 1.
Procedure: (Activity 1)
Ask the students what they know about root growth and stem growth on Earth. Ask them to predict what might happen to the responses of roots and stems in a weightless environment. Now have them set up the following experiment to verify their predictions about the responses of roots and stems on Earth.
Fill three test tubes with water. Carefully place the root end of a lima bean seedling through the hole of a stopper so that the stem end is at the top of the stopper. Seal the hole with a little wax or clay. Place the stopper into a test tube. Repeat this procedure for the other two plants. Clamp the test tubes onto a ring stand as shown in the diagram below. After a few days have the students check to see what responses the roots and stems have exhibited. How are the stems growing? The roots? What stimulus do the roots seem to respond to?
Let the students germinate seeds between a paper towel and the inside of a glass container. After germination, note the position of the roots and stems. Have the students turn the apparatus on its side and observe the response of the roots and stem after a few days. What happened to the direction of these? Try turning the containers different amounts every few days. What happens to the roots and stems?
You can compare the effect of gravity on several kinds of plants if you would like by doing the following: Prepare six containers as in activity 2, placing three bean, three radish and three corn seeds in each container. After germination, turn two containers on their sides and two upside down. Leave two alone as a control. Observe the response of the stems and roots after several days. The students by now should be able to conclude that roots and stems respond to gravity. You may want to try some of these in the dark, if the students have not already suggested this, to control for the response to light. Have the students hypothesize what the response of roots and stems might be in a weightless environment.
Teacher Note: Experiments on the Skylab growing wheat seeds showed that geotropic plants were a bit confused by the weightlessness of space. Roots and stems grew in all directions. It was apparent that if plants were to be grown in space that a system for providing artificial gravity would have to be employed. If some of your students have been to Epcot Center, ask them if they saw the experiments in the Plant World pavilion. Several experiments are underway there for NASA.
(Activity 3): Attach soilless containers similar to those in activity 1 to the turntable of a phonograph. Observe the growth of roots and stems now. Does the spinning motion’ of the turntable produce an artificial gravity? Do the plants behave in the same way as they did in activity 1? How are they the same or different?